Vertiv Liebert PEX4 Series

Questions and Answers

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hcruzAug 3, 2025
What to do if Vertiv Liebert PEX4 compressor cannot start?
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  Steven LopezAug 3, 2025
  If the Vertiv Air Conditioner compressor fails to start, begin by checking the main power switch, fuse, circuit breaker, and wiring to ensure power is connected. If the power is overloading and the MCB has tripped, manually reset it and check the average current value. Also, verify that all circuit connectors are firmly connected. Finally, check for static resistance imbalance in the motor windings, which could indicate a short circuit due to motor winding burnout, and replace the motor if necessary.
A
Anthony PetersAug 18, 2025
What to do if Vertiv Liebert PEX4 Air Conditioner compressor stops after 5 minutes?
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  Donna JacksonAug 18, 2025
  If the Vertiv Air Conditioner compressor stops operation for 5 minutes, it may be due to refrigerant leakage or too low voltage detection/abnormality. Check the suction pressure, the wiring of the low-pressure sensor, and ensure the differentiation between low pressure sensor reading and the actual pressure are within ± 0.3 bar.
K
kellymitchellAug 28, 2025
Why is there no heating effect in my Vertiv Liebert PEX4 despite the contactor being closed?
- J
  Jessica VelezAug 28, 2025
  If your Vertiv Air Conditioner's contactor is closed but there's no heating effect, the issue might stem from a main power failure of the heater. Check if the air switch heating system is closed or not. If the contactor is closed, check heating engaged state of contactors L1, L2 and L3 supply voltages is normal. Alternatively, the heater itself may be burned out. To check this, cut off the power supply and use an ohmmeter to check if the electrical heater is damaged by checking the resistance.
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Tiffany GibsonNov 7, 2025
How to troubleshoot Vertiv Liebert PEX4 Air Conditioner when humidification is ineffective?
- L
  Laura SimpsonNov 7, 2025
  To troubleshoot ineffective humidification in your Vertiv Air Conditioner, first, check the water supply to ensure there is water in the water pan, verifying the water supply solenoid valve is working, and inspecting the high water-level switch and water level regulator. Also, check the water supply pipe for clogs. If these are fine, check if the humidification contactor does not close, examine the opened safety devices of the infrared humidifier, such as the water pan over-temperature protection switch and lamp over-temperature protection switch. Check the voltage between terminal J18-2 and G on terminal row, if it is 24 V, then check the resistance of protection switch and replace if the resistance is very high. Further, check for humidifier main power failure by ensuring the humidifier ...
T
timothyhallNov 12, 2025
Why Vertiv Liebert PEX4 EC fan cannot be started?
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  David DicksonNov 12, 2025
  The Vertiv Air Conditioner EC fan might fail to start due to several reasons. It could be due to a fan power supply failure, so check if the fan MCB is closed and verify the phase voltage is normal. Another cause could be a control board failure; check if the output percentage of fans are 0, if not, check terminal J64 (1-Bay unit) or terminal J64 & J86 (2-Bay unit) is/are analog output of 0 Vdc to 10 Vdc, if so, replace the control board. A fan power module failure could also be the cause; check the alarm indicator of the fan power module. Also, check for a loss of airflow alarm and ensure the alarm default temperature difference value is appropriately set (10 °C plus is suggested). Lastly, an EC fan fault itself could be the issue; check if the fans L1, L2 and L3 are power-off, or have ph...
E
eric10Nov 22, 2025
What causes the heating system of Vertiv Liebert PEX4 to not operate and the contactor not to close?
- X
  xstarkNov 22, 2025
  If the heating system in your Vertiv Air Conditioner does not operate and the contactor does not close, several potential causes exist. First, check the PACC controller’s status to confirm whether there is a heating demand. Second, inspect the heating auxiliary relay for faults, checking if the light next to the relay is on and ensuring the wiring is correct. Finally, examine the heating system safety device for failure, using a multimeter to check J21-1 (for single electrical heating), J21-2 (for two electrical heating), and if the voltage across the terminals G is about 24 V, then move further to safety means across the resistor and if the resistance is large, it indicates that the security device must be disconnected. Check if the manual reset switch is turned off in case of the reset s...

Summary

Document Overview and History

Purpose of the Document

Explains the document's scope and applicability to the Liebert PEX4 series.

Styling Used in this Guide

Defines the visual styles used in the manual for warnings and notes.

Version History

Records past versions and revisions of the user manual.

Safety Precautions and Measures

General Safety Precautions

Outlines essential safety precautions for installation, operation, and maintenance.

Chapter 1: Product Overview

1.1. Product Introduction

Introduces the Liebert PEX4 series precision air conditioning system and its applications.

1.2. Model Description

Details the models, appearance, components, and configurations of the Liebert PEX4 series.

1.3. Model Nomenclature

Explains the model nomenclature and configuration options for the Liebert PEX4 series.

1.4. Components of PEX4 Model

Details components like Cabinet, Air Filter, EC Fans, Compressor, EMI Filter, Refrigeration Circuit, EEV, Evaporator Coil.

1.4.1. Cabinet

Describes the construction materials, finish, and internal sections of the PEX4 unit cabinet.

1.4.2. Air Filter

Explains the filter type, efficiency standards, and clog warning indication.

1.4.3. EC Fans

Details the EC fan specifications, including type, efficiency, IP rating, and mounting for down-flow.

1.4.4. Inverter Scroll Compressor

Describes the inverter-driven scroll compressor, its speed range, and energy efficiency benefits.

1.4.5. Oil Return Arrangement

Explains the intelligent oil return logic for proper compressor lubrication during part load.

1.4.6. EMI Filter

Details the built-in EMI filter for suppressing interference from the inverter drive system.

1.4.7. Refrigeration Circuit

Describes the direct expansion type refrigeration system, components, and safety notes.

1.4.8. Electronic Expansion Valve (EEV)

Explains the EEV function for modulating refrigerant flow, ensuring energy savings and superheat control.

1.4.9. Evaporator Coil

Details the parallel flow tube evaporator, its material, design, and configurations.

1.4.10. Dehumidification- EC Fan

Explains the dehumidification process using EEV control logic.

1.4.11. Remote Air-Cooled Condenser

Refers to specific user manuals for remote air-cooled condenser information.

1.4.12. Water-Under-Floor Sensor

Mentions the standard water under-floor detector and its alarm function.

1.4.13. Controller

Describes the controller's PID technology, self-recovery, and communication capabilities.

1.4.14. Color Display and HMI Features

Details the 9-inch color display, menu operations, and HMI features for monitoring and control.

1.4.15. Monitoring

Explains connection to BMS/BAS using Modbus RTU or SNMP protocols.

1.5. Additional Features

Introduces various optional features available for the PEX4 units.

1.5.1. Humidifier

Describes the two types of humidifiers: Infrared and Electrode.

1.5.2. Electrical Heating

Details the PTC heaters, their capacity, and safety devices used.

1.5.3. Upflow Plenum

Explains the upflow plenum, its grills, and material used for airflow regulation.

1.5.4. Long Piping Kit (Air Cooled System)

Describes the mandatory long piping kit for field piping lengths exceeding 30m.

1.5.5. Smoke Detectors

Explains the function of smoke detectors for system shutdown and alarm activation.

1.5.6. Fire Detectors

Details the fire detector's function in checking return air temperature and triggering alarms.

1.5.7. High-Efficiency Filter

Mentions the F5 grade filter for high efficiency output and cleaner environments.

1.5.8. Low Temperature Kit

Explains the low temperature kit for cold region startups and specific installation scenarios.

1.6. Operating & Storage Environmental Requirements

Specifies operating and storage environmental requirements for the Liebert PEX4 unit.

1.6.1. Operating Requirements

Details ambient temperature, protection level, altitude, and voltage range for operation.

1.6.2. Storage Requirements

Outlines general requirements, humidity, ambient temperature, and storage time limits.

Chapter 2: Installation

2.1. Pre-installation

Covers transportation, movement, unpacking, and inspection before installation.

2.1.1. Transportation & Movement

Guides on safe transport options and methods for moving the Liebert PEX4 unit.

2.1.2. Unpacking

Provides step-by-step instructions for safely unpacking the equipment from its packaging.

2.1.3. Inspection

Details the inspection process to check for complete fittings and intact components.

2.2. Installation Preparation (Site Preparation)

Details requirements for the equipment room, including insulation and damp-proofing.

2.2.1. Equipment Room Requirements

Specifies requirements for a favorable equipment room environment, including heat insulation.

2.2.2. Installation Space Requirements

Defines necessary space for indoor and outdoor units, avoiding obstructions and ensuring airflow.

2.2.3. Maintenance Space Requirement

Specifies the minimum clearance needed around the unit for maintenance access.

2.2.4. Installation Tools

Lists generic tools and utilities required for installation and maintenance processes.

2.2.5. System Arrangement during Installation

Illustrates the refrigeration system arrangement diagram and its components.

2.2.6. System Installation Mode

Explains schematic diagrams for condenser installation based on relative positioning.

2.3. Mechanical Installation

Covers indoor unit dimensions, weight, and mechanical parameters.

2.3.1. Indoor Unit Size and Weight (Product Dimension)

Presents dimensions and operational weight for indoor units, and floor height requirements.

2.3.2. Dimension and Weight of Condenser

Refers to specific user manuals for condenser dimensions and weight information.

2.3.3. Base Plate Cut-out Position and Dimension

Provides dimensions and positions for base plate cut-outs for pipe and cable entry.

2.3.4. Position and Dimension of Air Outlet on Top Cover

Details the position and dimensions of air outlets on the top cover of upflow units.

2.3.5. Indoor Installation - Floor Stand

Details requirements for preparing and installing the floor stand for single and double units.

2.4. Installation Considerations

Provides precautions for outdoor unit installation, airflow, noise, and roof mounting.

2.5. Pipe Installation Unit (Air-cooled Units)

Lists the four types of pipe joints and considerations for piping processes.

2.5.1. Condensate Drain Piping Connection of the Indoor Unit

Explains the connection of condensate drain piping for the indoor unit and pipe diameter requirements.

2.5.2. Humidification Inlet Pipe Connection

Details connection requirements for water inlet pipes to humidifiers, including material types.

2.6. Refrigerant Piping Connection

Specifies pipe dimensions, wall thickness, and imperial equivalents for refrigerant lines.

2.6.1. Refrigerant Piping Connection General Principle

Explains general principles for refrigerant piping, including equivalent length and height differences.

2.6.2. Refrigerant Requirement

Details the required quality and quantity of refrigerant (R410a) for optimal system efficiency.

2.6.3. Copper Pipe Brazing Requirements

Outlines safety measures and procedures for copper pipe brazing, including nitrogen protection.

2.7. Lowering the Fan

Describes the procedure for lowering the EC fans in the downflow unit using a winch-based tool.

2.7.1. Removing Transportation Fixing Plate of Compressor

Explains how to remove L-shaped fixing plates from the compressor base after installation.

2.7.2. Removing of Fasteners of Infrared Humidifier

Instructs on removing the rubber string from the high water-level switch before unit operation.

2.7.3. Removing of Fasteners from Electrode Humidifier

Details steps to remove fasteners and position the electrode humidification bottle vertically.

2.7.4. Removing Pipe Fasteners

Instructs to remove pipe cushioning materials before power-on commissioning.

2.7.5. Installation Inspection

Provides a checklist for verifying mechanical installation aspects before electrical connection.

2.8. Electrical Installation

Explains electrical installation considerations, indoor wiring, and power line connections.

2.8.1. Installation Notes

Covers regulations, personnel qualifications, supply requirements, and safety for electrical work.

2.8.2. Wiring of Indoor Unit

Guides on locating electrical ports and connecting power cables for the indoor unit.

2.8.3. Connecting Control Cables

Explains connecting control cables to terminal blocks, referencing figures and cable specifications.

2.8.11. Electrical Installation Inspection

Checklist for confirming correct electrical installation after completion.

Chapter 3: Controller Operating Instruction

3.1. HMI Display

Describes the 9-inch color HMI display characteristics, including operation and fault diagnosis.

3.2. Light Indicator

Explains the meaning of different LED indicator colors for system status.

3.3. Start-Up Interface

Shows the initial display screen after the unit is powered on.

3.4. User Menu

Lists menu keys and their functional descriptions for navigating the system interface.

3.4.1. Password Interface

Guides on accessing the password interface for user login and parameter modification.

3.4.2. Menu

Guides on accessing menu options for viewing and setting the system state.

3.4.3. Alarm Menu

Explains how to view current and historical alarm records on the system.

3.4. Parameters; System Settings

Covers setting system parameters like protocol, baud rate, and date/time.

3.5. Unit Status

Overview of unit status, including temperature, humidity, pressure, power, and teamwork.

3.5.1. Temperature and Humidity Status

Displays current temperature and humidity readings and status information.

3.5.2. Power Information Display

Details how to view power-related information such as voltage and frequency.

3.6. Hardware and Software Information

Displays control and display software model and version information.

3.7. Remote Monitoring Mode

Explains supported methods for remote monitoring of the air conditioner.

Chapter 4: General Maintenance

4.1. Manual Operation Function

Describes the diagnostic function to manually turn components On/Off for checking.

4.2. Electrical Connection Inspection

Lists inspection items for electrical connections, including insulation tests and terminal checks.

4.3. Control Component Appearance Inspection

Guides visual inspection and function tests of control components and connections.

4.4. Water Leak Detector

Explains the placement and connection of water leak detection sensors.

4.5. Air Filter

Covers air filter efficiency, replacement, and reset procedures for service alarms.

4.6. Fan Kit Maintenance

Details regular checks for EC fan motor status, impeller, and clearances.

4.7. Infrared Humidifier Maintenance

Provides cleaning steps for the infrared humidifier water pan to ensure efficient operation.

4.8. Electrical Heater

Outlines inspection and maintenance steps for the electrical heater and its temperature switches.

4.9. Cooling System Maintenance

Specifies monthly inspection of cooling system components and water pipes every six months.

Chapter 5: Troubleshooting

5.1. Componentwise Alarm and Solutions

Presents alarms and solutions categorized by system components.

5.1.1. Fan Troubleshooting

Diagnoses and treats common issues with EC fans, including power supply and motor faults.

5.1.2. Heating System Troubleshooting

Provides diagnosis and handling processes for heating system operation and contactor issues.

5.1.3. Compressor and AC System Troubleshooting

Covers troubleshooting for compressor start issues, contactor problems, and system faults.

5.1.4. Infrared Humidifier Troubleshooting

Diagnoses and resolves issues with humidification effectiveness and high-temperature protection.